JP2007271332A - Air-fuel ratio operating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress exhaust gas deterioration by suppressing the effect of noise, etc. on the theoretical air-fuel ratio voltage, serving as an air-fuel ratio calibration value, as to an air-fuel ratio calculation device that measures and calculates the air-fuel ratio on an internal combustion engine. <P>SOLUTION: An output voltage from an air-fuel ratio detecting circuit is multiplied by a prescribed number and filter-processing is performed therefor, thereby setting an output conversion value with its solution increased. When a pump electric current is cut off, a plurality of determination values and counters, corresponding thereto are set, based on the conversion value; and each time the conversion value is renewed, it is determined whether the conversion value agrees with the determined value. If there is no agreement, the determined values and counters corresponding thereto are reset. If there is agreement, counters corresponding to the determination values are added up. Determined values, having first agreed for a prescribed number of times or more are stored as the theoretical air-fuel ratio voltage. Based on this ratio voltage, an output voltage from the detecting circuit is calibrated, at non-cutoff of the pump electric current and the air-fuel ratio is calculated. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an air-fuel ratio calculation apparatus that measures and calculates an air-fuel ratio of exhaust gas of an internal combustion engine, and more particularly to an air-fuel ratio calculation apparatus that suppresses exhaust gas deterioration due to variations in the calibration value of the theoretical air-fuel ratio.

  In general, in an internal combustion engine, the air-fuel ratio of exhaust gas is measured by a linear air-fuel ratio sensor provided in the exhaust pipe, and the amount of fuel injection is feedback-controlled so that this is close to the stoichiometric air-fuel ratio. In this way, harmful gases such as CO and NOx are efficiently purified by a three-way catalyst. In such a linear air-fuel ratio sensor, variations in the manufacture of circuits for detecting the air-fuel ratio and variations in temperature characteristics occur according to the pump current applied to the solid electrolyte wall, and it is necessary to correct this.

  As a conventional air-fuel ratio sensor correction method, for example, a method as disclosed in Patent Document 1 is known. As shown in the flowchart of FIG. 7, this method cuts off the pump current of the linear air-fuel ratio sensor when it is determined that the condition for stopping the air-fuel ratio feedback control is determined based on various signals (steps S1 and S2). The output value of the circuit that converts the pump current into a voltage signal is measured a plurality of times and averaged (steps S3 to S5), and a value obtained by subtracting the average value of the output values from the reference voltage corresponding to the theoretical air-fuel ratio is a correction value. The latest calculated value is backed up and stored immediately before the engine operation is stopped (steps S6 to S8). When the air-fuel ratio feedback control is not in the middle of the correction calculation, an air-fuel ratio detection value (digital value) is converted by the conversion table based on a value corrected by adding the correction value to the output value converted to the voltage signal. ) (Steps S9 to S11).

Japanese Patent Laid-Open No. 2001-221095

In the prior art described above, the theoretical air-fuel ratio voltage is calibrated by calculating a correction value based on the A / D value obtained by passing the voltage output from the air-fuel ratio detection circuit through the A / D converter. The A / D value includes variations due to individual differences in the air-fuel ratio detection circuit, effects of A / D conversion errors, noise, and the like, and therefore varies with a few LSB widths (2 to 3 bits of the minimum digit). Therefore, since the averaged correction value includes an effect due to variations, the calibrated theoretical air-fuel ratio voltage also shifts, affecting the exhaust gas, and the purification rate of the three-way catalyst. There was a problem of lowering. The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain an air-fuel ratio calculation device that suppresses variations in the calibration value of the theoretical air-fuel ratio and suppresses the influence on exhaust gas. .

  The present invention is arranged in an exhaust system of an engine, and when a voltage is applied, a linear air-fuel ratio sensor made of a solid electrolyte that generates a current, supplies the voltage to the linear air-fuel ratio sensor, and detects the generated current. An air-fuel ratio calculation device comprising an air-fuel ratio output circuit that generates an output proportional to the magnitude of the detected current, an output conversion means for filtering the sensor output detected by the air-fuel ratio output circuit to increase resolution, and an air-fuel ratio Means is provided for correcting the output from the output circuit.

  According to the present invention, regarding the theoretical air-fuel ratio voltage value used for calibration of the output voltage of the air-fuel ratio detection circuit, it is possible to obtain a theoretical air-fuel ratio voltage value with less variation in which the influence of voltage fluctuation factors such as noise is reduced. By calibrating the output voltage of the air-fuel ratio detection circuit using the theoretical air-fuel ratio voltage value, it becomes possible to calculate the air-fuel ratio more accurately, that is, advanced exhaust gas purification and fuel efficiency improvement. Is.

Embodiment 1 FIG.
Hereinafter, an air-fuel ratio calculating apparatus according to Embodiment 1 of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a configuration of an internal combustion engine as an air-fuel ratio calculating apparatus according to Embodiment 1 of the present invention. In addition, in each figure, the same code | symbol shows the same or equivalent part. In FIG. 1, the electronic control unit 1 is electrically connected to a fuel injection device 3 provided in an intake pipe 2 and can adjust the fuel injection amount by a drive signal to the fuel injection device 3.

  The fuel injected into the intake pipe 2 is combusted by the engine 4 and discharged to the exhaust pipe 5 as exhaust gas. The electronic control unit 1 is also electrically connected to a linear air-fuel ratio sensor 10 provided in the exhaust pipe 5 so that the air-fuel ratio of the exhaust gas discharged from the engine 4 can be measured by the linear air-fuel ratio sensor 10. it can. Further, the exhaust pipe 5 is provided with a three-way catalyst 6 to purify harmful components such as HC, CO and NOx contained in the exhaust gas. However, in order to efficiently purify the aforementioned harmful components, it is necessary to control the fuel injection amount to the stoichiometric air-fuel ratio.

The electronic control device 1 efficiently uses the three-way catalyst 6 by adjusting the fuel injection amount of the fuel injection device 3 to be the stoichiometric air-fuel ratio based on the air-fuel ratio measured and calculated by the linear air-fuel ratio sensor 10. Exhaust gas can be purified.
FIG. 2 is a diagram showing the configuration of the linear air-fuel ratio sensor and the electronic control unit of the air-fuel ratio calculation apparatus according to the present invention.

  In FIG. 2, the linear air-fuel ratio sensor 10 includes a storage body of a pump cell 11, a porous diffusion layer 12, an electromotive force cell 13, and a reinforcing plate 14. The pump cell 11 is formed of a stabilized zirconia element which is an oxygen ion conductive solid electrolyte material, and has porous electrodes 15 and 16 mainly formed of platinum on the front surface and the back surface thereof.

  Similarly, the electromotive force cell 13 is formed of a stabilized zirconia element, and has porous electrodes 17 and 18 formed mainly of platinum on the front surface and the back surface, respectively. This electromotive force cell 13 has the property that an electromotive force is generated when there is a difference in oxygen concentration between the electrodes based on the same principle as a conventional oxygen sensor. The pump cell draws oxygen into and out of the measurement chamber 19 when a pump current flows. There is a nature to do.

  The electronic control unit 1 includes an air / fuel ratio detection circuit 20 and a microcomputer 23. The air-fuel ratio detection circuit 20 further controls the pump current, converts the pump current into an electric signal as shown by the linear air-fuel ratio sensor characteristics of FIG. 3, and outputs the electric signal to the microcomputer 23. And a pump current cut-off circuit 22 that cuts off the pump current. The air-fuel ratio detection circuit 20 also has a function of detecting the temperature of the linear air-fuel ratio sensor from the current value flowing through the resistance in the linear air-fuel ratio sensor 10.

  The air-fuel ratio detection circuit 20 feedback-controls the pump current for the pump cell 11 so as to keep the electromotive force of the linear air-fuel ratio sensor 10 constant, that is, so as to keep the electromotive force cell 13 at an oxygen concentration equivalent to the theoretical air-fuel ratio. To do. At this time, since the pump current continuously changes corresponding to the air-fuel ratio, the air-fuel ratio can be measured from the pump current. As described above, the linear air-fuel ratio sensor 10 is made of an oxygen ion conductive solid electrolyte, and an electromotive force cell 13 that outputs an electrical signal corresponding to the oxygen concentration in the exhaust gas, and oxygen in accordance with the supplied pump current. And a pump cell 11 for moving ions.

  The air-fuel ratio detection circuit 20 outputs a pump current to the pump cell 11 so that the output from the electromotive force cell 13 becomes a set value, and outputs an air-fuel ratio signal corresponding to the pump current as a voltage. In addition, a pump current cutoff circuit 22 that forcibly sets the pump current to 0 by a pump current cutoff command is provided, and when the pump current is cut off, a voltage when the pump current corresponding to the theoretical air-fuel ratio is 0 is output, Calibrate it as the theoretical air-fuel ratio voltage.

  Further, the microcomputer 23 has an A / D converter 24 for digitally converting the output voltage from the current / voltage conversion circuit 21 of the air-fuel ratio detection circuit 20, and has a resolution conversion function for the A / D converted value; It has a function of filtering the value whose resolution has been converted. When the pump current is cut off, a command is sent to the pump current cut-off circuit 22 to cut off the pump current. Further, based on the filtered value, It has a function that can calibrate the fuel ratio voltage.

  FIG. 4 is a flowchart showing the operation of the microcomputer of the air-fuel ratio calculating apparatus according to Embodiment 1 of the present invention. FIG. 5 is a time chart showing various state changes such as the pump current, the filter processing calculation value Vf (n), the determination value setting, the counter state, etc. relating to the calibration process of the theoretical air-fuel ratio voltage value. Hereinafter, the operation of the microcomputer 23 will be described with reference to FIGS.

  First, in step 101, the microcomputer 23 converts the output voltage from the current / voltage conversion circuit 21 of the air-fuel ratio detection circuit 20 into a digital value by the A / D converter 24 to obtain an output value. Next, in step 102, the resolution is converted by multiplying the A / D converted value by a predetermined number. (For example, if the A / D converter provided in the microcomputer has 10 bits, it can be converted to a value equivalent to 12 bits by multiplying the A / D value by four times.)

Next, in step 103, the resolution-converted value is filtered. The filtering process is performed based on the following formula.
Vf (n) = (1-G) * Vf (n-1) + G * V (n)
Here, G is the filter gain, V (n) is the converted value calculated in step 102, Vf (n-1) is the previous filter processing calculation value, and Vf (n) is the current filter processing calculation value. Represents. The filter gain G (0 ≦ G ≦ 1) represents the calculation ratio between the previous filter processing calculation value Vf (n−1) and the conversion value V (n) calculated in step 102.

Next, at step 104, the microcomputer 23 determines whether or not to interrupt the pump current of the linear air-fuel ratio sensor 10. If the pump current is cut off, the process proceeds to step 105. If not, the process proceeds to step 114.
Next, at step 105, the microcomputer 23 outputs a pump current cutoff command to the pump current cutoff circuit 22, and the pump current cutoff circuit 22 cuts off the pump current of the linear air-fuel ratio sensor 10.

  Next, in step 106, the microcomputer 23 determines whether or not the pump current is interrupted when the previous process is performed. This is because it is determined in step 105 described above that the pump current is cut off, thereby shifting from the pump current non-cut-off state to the cut-off state. If the pump current has not been cut off in the previous execution of the process, the process proceeds to step 107. If it has been cut off, the process proceeds to step 108.

  Next, at step 107, a judgment value used for the theoretical air-fuel ratio voltage calibration process and a counter corresponding to each judgment value are set. First, in FIG. 5, the current filter processing calculation value Vf (n) is set as a determination value ZA50 (V), and a total of nine determination values are set up and down at intervals of 1 LSB around the determination value ZA50. . (ZA10 to ZA90 in FIG. 5 correspond to this.) Furthermore, nine counters corresponding to each judgment value are set, and the initial value is set to zero. (See the counter states ZCNTA1 to ZCNTA9 in FIG. 5)

Next, in step 108, the microcomputer 23 determines whether or not the current filter processing calculation value Vf (n) is outside the set determination value range. If the current filter processing calculation value Vf (n) is outside the set judgment value range, the process proceeds to step 109, and if it is within the range, the process proceeds to step 110.
Next, in step 109, the determination value and the counter are reset. When the current filter processing calculation value Vf (n) is smaller than the determination value ZA90, the current filter processing calculation value Vf (n) is reset as the determination value ZA71, and the upper side is set at an interval of 1LSB with reference to the determination value ZA71. A total of 9 determination values are set (6 and 2 on the lower side) (ZA11 to ZA91 in FIG. 5 correspond to this).

  Alternatively, when the current filter processing calculation value Vf (n) is larger than the determination value ZA10, the current filter processing calculation value Vf (n) is reset as the determination value ZA32, and the determination value ZA32 is used as a reference at 1 LSB intervals. Then, a total of nine determination values are set (upper two and lower six) (ZA12 to ZA92 in FIG. 5 correspond to this). Further, for the counters corresponding to the respective determination values, the count results so far are initialized and correspond to the newly reset determination values. In FIG. 5, when the determination value is reset from ZA10 to ZA90 to ZA11 to ZA91 or reset from ZA11 to ZA91 to ZA12 to ZA92, the previous results of the counters ZCNTA1 to ZCNTA9 are returned to 0, and new determination values are set. The part (counter / judgment resetting process) that has been recounted based on this corresponds to this.

  Next, in step 110, the microcomputer 23 sequentially determines which of the determination values ZA1 * to ZA9 * the current filter processing calculation value Vf (n) matches. Next, at step 111, 1 is added to the numerical value of the counter corresponding to the determination value whose value coincides with the current filter processing calculation value Vf (n) at step 110 described above. For example, when Vf (n) = ZA3 *, 1 is added to the numerical value of the counter ZCNTA3.

  Next, in step 112, the microcomputer 23 determines whether or not the counter value processed in step 111 has reached a predetermined value. When the predetermined value is reached, the process proceeds to step 113. Specifically, when the predetermined value is set to 5 times, when the value of the counter added in step 111 becomes 5 times, the process proceeds to step 113.

Next, at step 113, the determination value corresponding to the counter that has reached the predetermined number is updated and stored as a new theoretical air-fuel ratio voltage value (theoretical air-fuel ratio voltage calibration process). Further, when this process is performed, the theoretical air-fuel ratio voltage value is prohibited from being updated until the pump current again shifts from the non-blocking state to the blocking state.
Next, at step 114, the air-fuel ratio is calculated from the difference between the theoretical air-fuel ratio voltage value described above and the filter processing calculation value calculated at step 103.

  FIG. 6 is a time chart comparing the operation of the prior art with respect to the output voltage (analog value) from the air-fuel ratio detection circuit 20 and the first embodiment of the present invention. In FIG. 6, the upper part is a waveform showing the conversion result of the output voltage from the air-fuel ratio detection circuit. From the air-fuel ratio detection circuit and the region where the change amount of the output voltage from the air-fuel ratio detection circuit 20 is large due to noise or the like. Are divided into regions (right side) where the output voltage is stable. The lower part shows the calculation result based on the output voltage change shown in the upper part.

  Further, in the upper part of FIG. 6, the solid line indicates the output voltage (analog value) from the air-fuel ratio detection circuit, the dotted line indicates the A / D conversion value of the output voltage from the air-fuel ratio detection circuit, and the minute dotted line indicates the filter processing calculation value. Vf (n) [set G = 0.5] is shown. In the lower part of FIG. 6, the black diamonds indicate the theoretical air-fuel ratio voltage values updated according to the present invention, the white circles indicate the judgment value / counter reset processing Vf (n), and the black circles. The mark indicates Vf (n) where the determination value / counter resetting process is not performed.

  In the case of the prior art, the theoretical air-fuel ratio correction value is calculated based on the A / D conversion value. The A / D conversion value is calculated by the A / D conversion error by the A / D converter 24 as described above. Deviation occurs with respect to the actual output voltage (analog value). As shown in the upper part of FIG. 6, the output voltage (analog value) indicated by the solid line and the A / D conversion value indicated by the broken line have a deviation with respect to the ALS conversion of 1 LSB or less. Arise. Furthermore, if the output voltage changes greatly due to factors such as noise, the A / D conversion error described above may have an effect, resulting in a large value with respect to the actual change in the output voltage (analog value). That is, as shown in the upper part (left side) of FIG. 6, in a region where noise or the like is generated, a phenomenon in which the change amount of the A / D conversion value is larger than the change amount of the output voltage (analog value) occurs. Yes.

  In contrast, in the first embodiment of the present invention described above, in step 102, the A / D conversion value is first multiplied by a predetermined number (for example, four times) to convert the resolution, and further in step 103, the filter processing is performed. By obtaining the filter processing calculation value Vf (n) to which is added, a large voltage change due to noise or the like can be reduced, and the voltage change amount can also be expressed with a resolution of 1 LSB or less of A / D conversion. That is, the dotted line shown in the upper part (right side) of FIG. 6 corresponds to the filter processing calculation value Vf (n).

  Further, in the method of obtaining the theoretical air-fuel ratio voltage by the average value of the A / D conversion values as in the prior art, if there is a large voltage change due to noise or the like as shown in FIG. It is also reflected in the average value. As shown by the solid line in the lower part of FIG. 6, the calculation is performed except for the average value of the entire A / D conversion values in the prior art and the region where the voltage change is large as shown by the dashed line on the lower part (right side). It can be seen that a deviation occurs in the average value of the A / D conversion values. Therefore, this becomes a variation factor of the theoretical air-fuel ratio voltage value, and a deviation occurs in the air-fuel ratio calibrated with the theoretical air-fuel ratio voltage value.

  On the other hand, in the calculation method of the theoretical air-fuel ratio voltage value according to the first embodiment of the present invention, since the determination value is set based on the output conversion value Vf (n) in step 107, it is set in steps 108 and 109. The output conversion value Vf (n) outside the range of the determination value can be excluded from the calculation target of the theoretical air-fuel ratio voltage value as an influence due to the change of the output voltage due to noise or the like. In addition, by setting a determination value in which the determination value and the output conversion value Vf (n) coincide with each other a predetermined number of times in a series of steps 110, 111, 112, and 113 as a theoretical air-fuel ratio voltage, the variation range is limited. The value which can be taken frequently in the specified range is adopted.

  As shown in the lower part of FIG. 6, the updated theoretical air-fuel ratio voltage (black diamond) adopted in the first embodiment of the present invention is a region where the output voltage from the air-fuel ratio detection circuit is stable. It can also be seen from the fact that it matches the average value of the part. Therefore, it is possible to obtain a theoretical air-fuel ratio voltage value with less variation that eliminates the influence of voltage fluctuations such as noise.

It is a figure which shows the structure of the internal combustion engine as an air fuel ratio calculating apparatus concerning this invention. It is a figure which shows the structure of the linear air fuel ratio sensor of the air fuel ratio calculating apparatus concerning Embodiment 1 of this invention, and an electronic controller. It is a figure which shows the linear air fuel ratio sensor characteristic of the air fuel ratio calculating apparatus same as the above. It is a flowchart which shows operation | movement of the microcomputer of an air fuel ratio calculating apparatus same as the above. It is a time chart which shows the change of the various states in the calibration process of a theoretical air fuel ratio voltage value. It is a time chart which shows the comparison of operation | movement of the prior art when the same output voltage from an air fuel ratio detection circuit is given, and Embodiment 1 of this invention. It is a flowchart which shows the correction control of the conventional air fuel ratio calculating apparatus.

Explanation of symbols

1 electronic control unit, 2 intake pipe, 3 fuel injection device,
4 engine, 5 exhaust pipe, 6 three way catalyst,
10 linear air-fuel ratio sensor, 20 air-fuel ratio detection device,
21 current / voltage conversion circuit, 22 pump current cutoff circuit,
23 Microcomputer, 24 A / D converter.

Claims (5)

  A linear air-fuel ratio sensor composed of a solid electrolyte that generates a pump current when a voltage is applied to the engine's exhaust system, and supplies the voltage to the linear air-fuel ratio sensor and detects the generated pump current. An air-fuel ratio calculation comprising a current / voltage conversion function for generating a voltage output proportional to the magnitude of the measured current and an air-fuel ratio detection circuit having a pump current cutoff command function for cutting off the pump current of the linear air-fuel ratio sensor In the apparatus, as means for correcting individual differences of the air-fuel ratio detection circuit, output conversion means for increasing the resolution of the voltage output output from the air-fuel ratio detection circuit, and means for correcting the output from the air-fuel ratio detection circuit are provided. An air-fuel ratio arithmetic device characterized by the above.   2. The air-fuel ratio arithmetic apparatus according to claim 1, wherein the output voltage value is multiplied by a predetermined constant and subjected to filter processing as means for increasing the resolution of the voltage output output from the air-fuel ratio detection circuit.   As means for correcting the output from the air-fuel ratio detection circuit, when the linear air-fuel ratio sensor transitions from the pump current non-blocking state to the blocking state, a plurality of determination values based on the output voltage value converted to the output, Set a counter corresponding to each judgment value, count which judgment value the output voltage value converted by the output conversion matches when the pump current is cut off, and theoretically decide the judgment value when the count first exceeded the predetermined number The air-fuel ratio calculation device according to claim 1, wherein the air-fuel ratio calculation device stores the air-fuel ratio voltage and corrects the output voltage value from the air-fuel ratio detection circuit.   When counting which judgment value the output voltage value converted by the output conversion matches when the pump current is cut off, the output voltage value converted by the output is greatly fluctuated and does not match any judgment value. 4. The air-fuel ratio calculation apparatus according to claim 3, wherein the determination value and the counter are reset.   The linear air-fuel ratio sensor is composed of an oxygen ion conductive solid electrolyte, and includes an electromotive force cell that outputs an electric signal according to the oxygen concentration in exhaust gas, and a pump cell that moves oxygen ions according to a supplied pump current. The air-fuel ratio calculation apparatus according to claim 1, further comprising:

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